The present invention relates to a radiation sensitive composition containing a specific pigment. More specifically, it relates to a radiation sensitive composition which can be advantageously used for the production of an additive or subtractive color filter to be used in a reflection-type color liquid crystal display device.
In color filters used in a color liquid crystal display device, two or more different color pixels are arranged in parallel to one another or across one another to form a striped pixel pattern, or in both horizontal and transverse directions to form a square pixel pattern on the surface of a transparent substrate such as glass. The pixel is as minuscule as several tens to several hundreds of micrometers.
To produce a color filter having such minuscule pixels arranged regularly, there have been employed a dying method in which a coating film formed by coating a photosensitive resin on a substrate is exposed to radiation through a photomask to cure exposed portions and developed, and after unexposed portions are removed to form a pattern, the pattern is dyed; a photolithography method in which a coating film is formed using a composition comprising a photosensitive resin and a colorant (dye or pigment) dispersed or dispersed therein, exposed and developed in the same manner as in the dying method to form a pattern; and the like.
In a color liquid crystal display device, a transparent electrode made from indium oxide, tin oxide or the like is formed on a color filter by vapor deposition or sputtering and an alignment layer for aligning liquid crystals in a fixed direction is further formed on the transparent electrode so as to drive the liquid crystals. To obtain a high-performance transparent electrode and alignment layer, a high temperature of 200xc2x0 C. or higher, preferably 250xc2x0 C. or higher is required when these are formed.
Of color filters manufactured by the above methods, a color filter produced by using a dye has high transparency to radiation but is insufficient in terms of heat resistance. Therefore, this method has a problem in that the formation of a transparent electrode and an alignment layer must be carried out at a temperature lower than 200xc2x0 C., thereby making it impossible to ensure sufficient performance for the transparent electrode and alignment layer. A color filter produced by using a dye is also inferior in light resistance and hence not suitable for outdoor use.
Then, a pigment has recently been used in place of a dye, and most of color filters currently manufactured comprise an organic pigment.
Color liquid crystal display devices are roughly divided into transmission-type color liquid crystal display devices which display images with transmission light from a backlight installed at the back of the device and reflection-type color liquid crystal display devices which display images by reflecting incident light coming from the front of the device with a reflector such as an aluminum foil provided on the reverse of a transparent substrate installed at the back of the device. The reflection-type color liquid crystal display devices have been widely used because they have such an advantage that another separate light source is not required and power consumption is low.
Color filters to be used in color liquid crystal display devices are available in additive color filters having three primary colorsxe2x80x94red (R), green (G) and blue (B)xe2x80x94and subtractive color filters having three colors complementary to the primary colorsxe2x80x94cyan (C), magenta (M) and yellow (Y).
JP-A 9-68608 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses that a color filter having excellent heat resistance and light resistance and color purity equal to or higher than that of a color filter produced by the dyeing method can be formed by using a specific azo metal salt pigment or a mixture of the pigment and a yellow pigment as a colorant for a coloring composition for use in a reflection-type color liquid crystal display device.
However, since the relationship between the spectral transmittance of the colorant used and the spectrum of surrounding light (such as sunlight and fluorescent light) is not taken into consideration in this coloring composition and the coloring composition is inferior in white balance, the composition is still unsatisfactory as a coloring composition used for the formation of a color filter for a reflection-type color liquid crystal display device.
Therefore, the development of an additive color filter to be used in a reflection-type color liquid crystal display device which has heat resistance, light resistance and spectral transmittance optimized based on the spectrum of surrounding light as well as a subtractive color filter to be used in a reflection-type color liquid crystal display device which has heat resistance, light resistance and excellent white balance has been strongly desired.
It is therefore an object of the present invention to provide a radiation sensitive composition containing a specific pigment.
It is another object of the present invention to provide a radiation sensitive composition which is advantageously used for the production of an additive and/or subtractive color filter having excellent heat resistance and light resistance and spectral transmittance optimized to suit the spectrum of surrounding light.
It is still another object of the present invention to provide a radiation sensitive composition which is advantageously used for the production of a subtractive color filter having excellent heat resistance, light resistance and white balance.
It is still another object of the present invention to provide a radiation sensitive composition which is advantageously used for the production of the above color filters to be used in a reflection color liquid crystal display.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention can be attained by a radiation sensitive composition (may be referred to as xe2x80x9cthe first radiation sensitive composition of the present inventionxe2x80x9d hereinafter) comprising:
(A1) a colorant containing a quinacridone pigment represented by the following formula (1): 
wherein R1 to R8 are independently a hydrogen atom, a methyl group or a chlorine atom;
(B) an alkali-soluble resin;
(C) a polyfunctional monomer; and
(D) a photopolymerization initiator.
Secondly, the above objects and advantages of the present invention can be attained by a radiation sensitive composition (may be referred to as xe2x80x9cthe second radiation sensitive composition of the present inventionxe2x80x9d hereinafter) comprising:
(A2) a colorant containing a mixture of an isoindolinone pigment represented by the following formula (2) and a yellow organic pigment; 
(B) an alkali-soluble resin;
(C) a polyfunctional monomer; and
(D) a photopolymerization initiator.
Thirdly, the above objects and advantages of the present invention can be attained by a radiation sensitive composition (may be referred to as xe2x80x9cthe third radiation sensitive composition of the present inventionxe2x80x9d hereinafter) comprising:
(A3) a colorant containing copper phthalocyanine blue represented by the following formula (3): 
and at least either one of a green pigment represented by the following formula (4): 
and a green pigment represented by the following formula (5): 
in an amount of 50 wt % or less, based on the total weight of the copper phthalocyanine blue and the green pigments;
(B) an alkali-soluble resin;
(C) a polyfunctional monomer; and
(D) a photopolymerization initiator.
The term xe2x80x9cradiationxe2x80x9d as used in the present invention includes visible light, ultraviolet light, far ultraviolet light, X-ray, electron beam and the like.